ABI2, A 2ND PROTEIN PHOSPHATASE 2C INVOLVED IN ABSCISIC-ACID SIGNAL-TRANSDUCTION IN ARABIDOPSIS

The abi2-1 (abscisic acid insensitive) mutant of Arabidopsis thaliana shows abscisic acid (ABA) insensitivity with respect to seed germinati on and vegetative ABA responses, We identified the ABI2 gene by a comb ination of positional mapping and homology to ABI1. The ABI2 protein s hoes 80% amino acid sequence identity to ABI1, a protein phosphatase 2 C (PP2C) involved in ABA signaling. The mutation that confers the abi2 -1 phenotype is equivalent to the mutation previously identified in ab i1-1 and the resulting Gly(168)Asp abi2 protein shows a reduced PP2C a ctivity. Thus, a pair of highly homologous PP2Cs regulate ABA signalin g. (C) 1998 Federation of European Biochemical Societies.